Until recently, as refrigeration engineers looked at ways to increase system efficiency, the emphasis was on the portion of the system that was outside the refrigerated space, the compressor-condenser equipment. There are exceptions to this, as in the case of VFD controlled evaporator fan motors being used in a relatively small percentage of industrial systems and other fan control systems in both commercial and industrial applications. With some of this equipment, the energy consumption at the evaporator fans could be reduced by more than 80 percent, once the thermostat set point is reached. On an average year, that would mean the fan motors could be operating at this reduced level 60 percent of the time.
Over the past three years, Electronically Commutated Motors, ECM, have been making a significant impact toward saving energy and thereby reducing operating costs. They are especially popular in the replacement of small shaded pole motors up to 1/15hp. These are the fan motors most commonly found in grocery stores and restaurants. This change alone will provide a 50 to 55 percent reduction in direct energy consumption but a 50 percent reduction in watts also means less heat generated inside the refrigerated space and reduced compressor run time.
Unfortunately, too many have assumed that switching out old shaded pole motors for single speed EC motors was as far as they could go, and in some cases this is correct. However where the load per motor equals 1.7 amps or more on 115 volt service or half that on 230 volt service, substantial additional savings can be achieved through the use of two-speed EC motors. To illustrate this, coil manufacturers will often show the amperage per motor at 2.1 on 115 volt service. That shaded pole motor will be consuming 150 watts of power. The ECM replacement will draw only 46 percent of that or 69 watts. As a two speed motor with the low speed reduced from 1550 to 600 RPM, its consumption will only be 6 watts and if the original duty cycle was 40 percent, it will now become closer to 30 percent due to the reduction in fan motor heat, (1 watt equals 3.4 Btu). The savings are obvious but just how much can be saved and what will be the ROI? Programs are available to estimate, reliably, just how much should be saved.
EC motors are readily accessible in sizes to ¾hp and 230 volts but very soon 460 volt models to one horsepower will become available. Where sizes are 1/5hp and larger, the savings must be considered differently than in the previous paragraphs where shaded pole motors were referenced. In these sizes, the replaced motors are PSC type, or even three-phase motors and as such, much more efficient than the shaded pole motors. Economics dictate that these motors be speed controlled. With that combination, ECM and controller, the return on investment can be even shorter than when replacing inefficient shaded pole motors.